Along with compactization of electronic instruments, there is an increasing demand for a compact, thin and light-weight battery. On the other hand, there is a demand for a battery having high energy density and high energy efficiency, and thus a secondary battery such as an Li ion battery is drawing attention. In response to these demands, a proposal has been made, for example, in JP-A-61-240564, in which a sealed lead battery is produced in such a manner that electrode arrays are inserted in a bag made of a thermoplastic resin having acid resistance, and a plurality of the electrode arrays are wrapped with an outer sheath in the form of a bag comprising a synthetic resin in the form of a film, a sheet or a tube.
There are other proposals in JP-A-3-62447 and JP-A-57-115820, in which the hermetic property is improved by using a sheet of the sealing bag having a structure, in which a metallic layer is sandwiched between plastic films.
The provision of the metallic layer greatly improves the hermetic property, but the invasion of water from a sealed part cannot be completely prevented. When water invades a battery, it reacts with an electrolytic solution to produce hydrofluoric acid, which passes through the plastic film layer, thereby likely corroding the metallic layer or promoting peeling between the metallic layer and the plastic layer. The reasons for the occurrence of peeling also is due to the use of a urethane-based adhesive as an anchor coating material for bonding the metallic layer and the plastic layer on the side of the electrolytic solution.